ATLANTA (CNN) -- Sleep apnea, narcolepsy, insomnia: these are just a few of the recognized disorders that keep their afflicted from getting enough sleep. Nearly half of all Americans have difficulty sleeping.

Some people may show great bravado about getting a job done on little sleep. Some even brag about having trouble sleeping, claiming their work proves they didn't need the rest anyway. Yet the truth is that fatigue is dangerous. A growing collection of research indicates that America's sleep problems have reached epidemic proportions, and may be the country's number-one health problem.

We don't know what sleep is. We do know we need it to survive. Sleep restores us. Those who sleep fewer than six hours a night don't live as long as those who sleep seven hours or more.

Lack of sleep can be expensive: The National Commission on Sleep Disorders estimates that sleep deprivation costs $150 billion a year in higher stress and reduced workplace productivity.

It may also lead to personal and public tragedy. There are indications that the Challenger disaster, the Chernobyl nuclear reactor meltdown and the Exxon Valdez oil spill can all be partly linked to people suffering from a severe lack of sleep.

Dr. Serena Koenig, 13 hours into a 36-hour shift at Brigham and Women's Hospital in Boston, admits that her grueling schedule allows no room for error.

"You do not have the luxury of being tired. You have to take care of that patient," she said. "If you make a mistake, that patient could be hurt by it and the fear of making mistakes keeps you clear thinking. I have never made a mistake because I have been tired."

Her hospital pays close attention to problems associated with sleep deprivation among health care workers, but only recent research has shown that sleeplessness is a major problem in many fields of work.

Pete Filbrick has been a truck driver for 30 years. He, too, has never made a mistake. But he knows what can happen.

"I haven't seen the figures on that, but I would think fatigue would play a pretty big role in almost any accident," Filbrick said.

Figures suggest that driver fatigue contributes to 30 to 40 percent of all heavy truck accidents. Many truckers simply can't recognize the point that their bodies are tired enough for them to fall asleep.

Dr. David Dinges studies sleep at the University of Pennsylvania. He says almost every study that has looked at the timing of crashes across the day shows that at least for fall-asleep crashes, there are huge peaks in the middle of the night and smaller peaks in the middle of the afternoon.

"It's clear that the same biological forces that regulate brain function are contributing to fall-asleep crashes on the roadway," he said, pointing out that some of the more serious industrial catastrophes, from Three Mile Island to the Exxon Valdez, "occurred on the night shift and involved some sort of human error."

On Sunday, at 4:30 in the afternoon -- one of those peak times the body prefers to shut down -- part of Frank Salvaggio's brain apparently shut down.

"I remember one thing only. One second before impact, I can see the other driver's face. The cars are head to head and they are about to make impact," Salvaggio said. "That was a very tragic accident."

Salvaggio killed a woman, and was tried for vehicular homicide. Dr. Charles Czeisler, who studies sleep at Brigham and Women's Hospital, testified at his trial. He said what happened to Salvaggio is known as Automatic Behavior Syndrome -- when one part of you falls asleep, the other part keeps on going. The syndrome has been a contributing factor in plane, train and car crashes.

"I would say that right now, the social consciousness of this country on the issue of sleeping and driving is the same place drinking and driving was 30 years ago," Czeisler said. (30 sec. /352K AIFF or WAV sound)

Meanwhile, prominent national figures are sending Americans the wrong message about work and sleep, doctors say. "Four years ago, when President Clinton was running for office, he very publicly proclaimed that he went the last 48 hours without sleep because he really wanted to become president," Czeisler said.

"What he was doing was setting a really bad example for people. He was saying that when you were trying to reach your goal, you can sacrifice sleep."

Former Senator Bob Dole did the same thing in his 1996 presidential campaign. "We have been going 78 hours. We've got to go 96. We have been going around the clock for America," he told the public toward the end of his campaign.

Yet if we have learned anything about sleep leadership since the campaigns of 1992 and '96, it is that America needs to be told to get a good night's sleep.